Fail-safe heating apparatus

ABSTRACT

Fail safe heating apparatus is disclosed in which a pair of heater elements are interconnected for normal operation to operate on half voltage and each element is connected to an alarm system in case a malfunction and in such case of malfunction, the remaining heater element takes full voltage and thus replaces the malfunctioned element.

United States Patent [191 Griffin FAIL-SAFE HEATING APPARATUS [76] Inventor: John W. Griffin, P.O. Box 566,

Page, Ariz. 86040 [22] Filed: Apr. 30, 1973 [21] Appl. No.: 355,868

[52] US. Cl 219/482, 13/24, 219/327, 219/350, 219/509, 340/371 [51] Int. Cl. ..l H05b 1/02 [58] Field of Search... 219/327, 350, 351, 480-486, 219/488, 502, 509; 307/24, 28, 38, 39; 340/251, 252 H, 253 B, 371; 13/24 [56] References Cited UNITED STATES PATENTS 3,180,999 4/1965 Kuykendall 219/508 [451 Apr. 16, 1974 3,050,611 8/1962 Kamide 219/480 Primary Examiner-J. D. Miller Assistant Examiner-Harry E. Moose, Jr. Attorney, Agent, or Firm-H. Gordon Shields [5 7] ABSTRACT Fail safe heating apparatus is disclosed in which a pair of heater elements are interconnected for normal operation to operate on half voltage and each element is connected to an alarm system in case a malfunction and in such case of malfunction, the remaining heater element takes full voltage and thus replaces the malfunctioned element.

6 Claims, 2 Drawing Figures FAIL-SAFE HEATING APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to heating systems, and, more particularly, to heating systems which include a pair of heating elements and an alarm system for each element.

2. Description of the Prior Art There are many industrial applications for heaters in which a malfunction of a heating element results in substantial damage or problems, such as in chemical or petrochemical plants. Ofter in such applications an alarm system is used in conjunction with a heating element such that a malfunction of the heating element, as for example the element burning out, results in an alarm going off. Alarms of these types are typically bells which ring and/or lights that flash. The sounding of the alarm gives notice of the malfunction and corrective measures are implemented to overcome the ma]- function. However, during the downtime of the heater, valuable time is lost and substantial damage to processes and materials may result. Moreover, it is often difficult and inconvenient to replace a heating element. Accordingly, a system is desired which includes fail safe provision for continuing to supply heat to allow whatever processes are desired to continue in the event of a heater malfunction. None of the prior art systems have such provision.

SUMMARY OF THE INVENTION This invention includes a pair of heating elements, each of which operate simultaneously, and in the event of a malfunction of a heating element, the other element takes over the heating function of the malfunctioned element. In normal operation, each heating element operates at half voltage and, should one element malfunction, the remaining element operates at full voltage. An alarm system is incorporated in the heating apparatus.

Among the objects of this invention are the following:

To provide a new and useful heating system;

To provide a new and useful fail-safe heating system;

To provide a new and useful heating system utilizing a pair of heating elements;

To provide a new and useful heating system in which a pair of elements operate at half voltage each under normal conditions;

To provide new and useful fail safe heating system which includes an alarm system; and

To provide a new and useful fail safe heating system employing a pair of heating elements and each element includes an alarm system and a current transformer to actuate each alarm system.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic circuit drawing showing the circuit employed in the present invention.

FIG. 2 is a schematic circuit representation of an alternate embodiment of a portion of the apparatus of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Heating apparatus embodying the present invention is schematically shown in FIG. 1. Line voltage is connected to the apparatus through terminals LI and L2. The apparatus comprises essentially a pair of circuits or systems, each of which is substantially a mirror image of the other, with the line voltage terminals L1 and L2 as the common denominator or common connection. However, the two systems are interconnected as will be described in detail. The two systems of the apparatus are respectively designated as first system 10 and second system 100. From terminal L1, a conductor 12 extends to thermostat contacts 14. Conductor 16 extends between thermostat contacts 14 and the positive terminal or anode of diode D1. A conductor 18 is connected to the negative terminal or cathode of diode D1.

For the second heating system 100, conductor 112 extends from terminal L1 to thermostat contacts 114. A conductor 116 extends between thermostat contacts 114 and the positive terminal or anode of diode D2.

Conductor ]l 18 is connected to the negative terminal or cathode or diode D2. Conductor 118 is connected to the negative terminal or cathode of diode D2.

While two pair of thermostat contacts 14 and 1 14 are shown, it will be understood that only one thermostat with two pair of contacts or the like may preferably be employed. If desired, two thermostats may be used.

A conductor 60 extends from terminal L2. One end of heating elements 20 and 120 of heaters number one and two, are connected to conductor 60 and the other end of each heating element is respectively connected to conductors l8 and 118.

With the circuitry as described thus far, each heater element will be on when thermostat contacts 14 and 114 call for heat and close the respective heater ele ment circuits. With diodes D1 and D2 allowing only half of the line voltage to pass, each heater element accordingly operates on only half voltage, but the total heat produced is the normal or desired amount.

Each heating system utilizes a current transformer to determine when current is flowing in conductors l2 and 112 respectively, such as when the thermostat contacts 14 and 114 call for the heating elements 20 and 120 to produce heat. At such times, the thermostat contacts close the circuits to allow current to flow in the respective conductors and components of the circuit. The first heating system 10 includes a current transformer 30, which comprises a pair of inductors 32 and 34 connected in parallel, with a capacitor 36 connected in parallel with them and disposed between them. A diode 38 is connected in series between the inductors and intermediate the inductor 32 and the capacitor connected together. Inductor 32 is wound about conductor 12 and senses the current flowing therethrough. Inductor 34 comprises a coil for an appropriate relay R1, which may preferably be a reed relay. Relay R1 includes a pair of relay contacts 40 which are normally closed.

When current flows through conductor 12 to heater element 20 of heater number one, the current transformer 30 senses the flow of current and relay contacts 40 of relay R1 open.

The second heating system 1100 also includes a current transformer. Current transformer of the second heating system is substantially the same as current transformer 30, and it includes a pair of inductors 132 and 134 connected in parallel with a capacitor 136 in parallel with the inductors and intermediate thereto. A diode 138 is connected between the inductors and intermediate inductor 132 and capacitor 136, with the positive leads or anodes of the diode and the capacitor connected together. Inductor 134 comprises a coil for relay R2, which is substantially the same as Relay R1. The relay R2 includes a pair of relay contacts 140 which are normally closed.

Relay contacts 40 in relay R1 are connected to a pair of conductors 42 and 44. Conductor 42 extends between one side of relay contacts 40 and conductor 116 of the second heating system. Conductor 44 extends from the other side of relay contact 40 and is connected to conductor 46 and conductor 48. Conductor 46 extends from conductors 44 and 48 to heater number 2 and conductor 118. Conductor 48 extends from conductors 46 and 44 to alarm system 50.

Alarm system 50 includes a warning light A] and an alarm bell 52. The warning light A1 and the bell 52 are connected in parallel with each other. One side of each is connected to conductor 48 and the other side of each is connected to terminal L2 through a conductor 56 which extends to conductor 60.

One end of relay contacts 140 in relay R2 of the second heating system is connected by a conductor 142 to conductor 16 of the first heating system. The other side of relay contact 140 is connected to conductor 144, which is in turn connected to conductors 146 and 148. Conductor 146 extends from conductors 144 and 148 to conductor 18 and heating element 20 of heater number one in the first heating system. Conductor 148 extends from conductors 144 and 146 to an alarm system 150 which includes a warning light A2 and a warning bell 152. The warning light and warning bell are connected in parallel with each other, with one side of each connected to conductor 148. The other side of the warning light and the bell is connected to terminal L2 through conductor 156 and conductor 60.

In operation, with line voltage connected to terminals L1 and L2 and the thermostat contacts 14 and 1 l4 and closed, calling for heat, current flows through the heating elements of heaters one and two, at half line voltage in each heater due to the blocking action of diodes D1 and D2. While current flows through conductors 12 and 112, current transformers 30 and 130 activate the relay coils 34 and 134 to open relay contacts 40 and 140.

If a malfunction occurs in a heater, as for example the heating element 20 of heater number one burning out and thus opening the circuit between conductors 18 and 60, no current would flow in conductor 12 and thus current transformer 30 would turn off. This would result in the closing of relay contacts 40. Current would accordingly flow through conductor 42 from conductor 116 of the second heating system through relay contacts 40 and through conductor 44 and conductors 46 and 48. With current flowing through conductor 48, warning light A1 would turn on and warning bell 52 would be activated. A hand actuated switch 54 is shown in series with warning bell 52 and may be used to manually turn off the bell after a malfunction has been detected by appropriate personnel.

Current flowing through conductor 46 is shunted around diode D2 in the second heating system to heating element of heater number two which accord ingly results in a full line voltage being applied to heater number two. With double the voltage in heater number two, the heating function of both heaters number one and number two is now completely and fully assumed by heater number two. This situation may continue until heating element number one has been replaced.

The same procedure as described in the preceding paragraph occurs if a malfunction happens in the circuitry of heater number two, as for example if element 120 of heater number 2 burns out causing the circuit to open. When the circuit opens, current ceases to flow in conductor 112 through current transformer 130. Accordingly, the current transformer turns off and relay contacts of relay R2 close. Warning light A2 and warning bell 152 are thus connected to terminal L2 through conductors 60 and 156, and to terminal Ll through conductors 148, 144, 142, and 12.

The warning light and warning bell thus alert appropriate personnel that a malfunction has occurred in the circuit of heater number two. Manual switch 154 allows the warning bell 152 to be disconnected, if desired.

Diode D1 is now shunted out of the heater circuit 10 with respect to heating element 20 of heater number one, and the heating element now receives full line voltage and accordingly the heating function of both heaters number one and number two is assumed by heater number one. Heater number two may now be repaired without causing downtime" and the corresponding loss of convenience or expense otherwise necessitated if heater element number one were not able to completely assume the function of both heating elements 20 and 120.

FIG. 2 discloses an alternate embodiment which may be required in some circumstances. If a heater element were to draw only a small amount of current, as in specialized applications, in place of a current transformer as described above, an amplifier 80 may be required to operate coil 234 of relay R3. As illustrated in FIG. 2, an inductor 232 is wound about a conductor 12 through which current flows to a heating element. The inductor is connected to the primary winding of amplifier 80. Inductor 234 is connected to the secondary winding of the amplifier. The inductor 234 comprises coil for an appropriate relay R3. When a small current is sensed in inductor 232, the current is amplified by amplifier 80 to the extent that sufficient current is available to actuate coil 234 of relay R3 to open relay contacts 240, which are normally closed. The relay contacts 240 are disposed between conductors 244 and 242 and they connect conductor 242 to conductor 246 and 248 by way of conductor 244. The contacts 240 and the respective connectors correspond to relay contacts 40, conductors 42, 44, 46 and 48 of FIG. 1. FIG. 2 is thus illustrative of an alternate embodiment of the apparatus of FIG. 1.

The circuitry above disclosed and described comprises a fail-safe heating apparatus which includes a first and a second heater system. Either heating system can assume by itself the heating function of the other in case of a malfunction of one of the systems. Under normal circumstances, each heater system operates on only half voltage, but in the event of a malfunction, as an open circuit, the remaining heater system operates on full voltage until the other system is repaired and again restored to its desired capacity. Under normal operating conditions and circumstances, current transformers are used to sense current flow through each heater system. If a heater system utilizesvery small currents, then a current amplifier may be required.

It will be noted that indicator lights A1 and A2 will be operating at half voltage during normal operation. Accordingly, the intensity of the lights will be very low. This, in and of itself, indicates that the apparatus, including both heating elements, is operating property.

.However, the half voltage is insufficient to operate the alarm bells 52 and 152. When a heating element malfunctions and accordingly the other heating element operates at full voltage, the appropriate warning light and warningbell receive full voltage and effect the ringing of the bell and the burning of the warning light at full intensity, thus signaling a malfunction.

While the principles of the invention have been made clear in illustrative embodiments, there will be immediately obvious to those skilled in the art many modifications of structure, arrangements, proportions, elements, materials, and components used in the practice of the invention, and otherwise, which are particularly adapted for specific environment and operative requirements without departing from those principles. For example, and not by way of limitation, the apparatus could include a pair of thermostats, one for each heating circuit, and each with its own paid of contacts for its associated circuit, rather than a single thermostat with a pair of contacts 'each heating circuit. The appended claims are intended to cover and embrace any and all such modifications, within the limits only of the true spirit and scope of the invention. This specification and the appended claims have been prepared in accordance with the applicable Patent Laws and the rules promulgated under the authority thereof.

What is claimed is:

1. Fail-safe heating apparatus comprising, in combination:

first and second terminals for providing a source of voltage;

a first heating circuit, including a first heating element connected between the first and second terminals,

first sensing means for sensing current flow between the first terminal and the first heating element,

first relay means, including a first pair of normally closed contacts, for holding said first pair of normally closed contacts open in response to the sensing current flow between the first terminal and the first heating element,

a first diode between the first terminal and the first heating element for limiting the voltage to the first heating element, a second heating system, including a second heating element connected between the first and second terminals,

second sensing means for sensing current flow between the first terminal and the second heating element,

second relay means, including a second pair of normally closed contacts, for holding said second pair of normally closed contacts open in response to the sensing of current flow between the first terminal and the second heating element,

a second diode between the first terminal and the second heating element for limiting the voltage to the second heating element;

first means for shunting the first diode to provide full voltage to the first heating element in response to the closing of the second pair of normally closed contacts in response to an interruption of the current flow between the first terminal and the second heating element as sensed by the second sensing means; and

second means for shunting the second diode to provide full voltage to the second heating element in response to the closing of the first pair of normally closed contacts in response to an interruption of the current flow between the first terminal and the first heating element as sensed by the first sensing means.

2. The apparatus of claim 1 in which the first and second sensing means for sensing current flows comprises a first and a second current transformer coupled respectively to the first relay means and to the second relay means.

3. The apparatus of claim 1 in which the first and second sensing means for sensing current flows comprises a first and a second current amplifier coupled to the first relay means and to the second relay means.

4. The apparatus of claim 2 in which the first means for shunting the first diode includes a conductor extending from between the first terminal and the first diode to one of the contacts of the second pair of normally closed contacts of the second relay means, and conductor means extending from the other contact of the second pair of normally closed contacts of the second relay means respectively to the second terminal and to the first heating element.

5. The apparatus of claim 4 in which the second means for shunting the second diode to provide full voltage to the second heating element includes a conductor extending from between the first terminal and .the second diode to one contact of the first pair of normally closed contacts of the first relay means and conductor means extending from the other contact of the first pair of normally closed contacts of the first relay means respectively to the second terminal and to the second heating element.

6. The apparatus of claim 5 in which the first heating circuit includes warning apparatus for sensing the interruption of current flow between the first terminal and the first heating element, and the second heating circuit includes warning means for sensing the interruption of current flow between the first terminal and the second heating element. 

1. Fail-safe heating apparatus comprising, in combination: first and second terminals for providing a source of voltage; a first heating circuit, including a first heating element connected between the first and seconD terminals, first sensing means for sensing current flow between the first terminal and the first heating element, first relay means, including a first pair of normally closed contacts, for holding said first pair of normally closed contacts open in response to the sensing current flow between the first terminal and the first heating element, a first diode between the first terminal and the first heating element for limiting the voltage to the first heating element, a second heating system, including a second heating element connected between the first and second terminals, second sensing means for sensing current flow between the first terminal and the second heating element, second relay means, including a second pair of normally closed contacts, for holding said second pair of normally closed contacts open in response to the sensing of current flow between the first terminal and the second heating element, a second diode between the first terminal and the second heating element for limiting the voltage to the second heating element; first means for shunting the first diode to provide full voltage to the first heating element in response to the closing of the second pair of normally closed contacts in response to an interruption of the current flow between the first terminal and the second heating element as sensed by the second sensing means; and second means for shunting the second diode to provide full voltage to the second heating element in response to the closing of the first pair of normally closed contacts in response to an interruption of the current flow between the first terminal and the first heating element as sensed by the first sensing means.
 2. The apparatus of claim 1 in which the first and second sensing means for sensing current flows comprises a first and a second current transformer coupled respectively to the first relay means and to the second relay means.
 3. The apparatus of claim 1 in which the first and second sensing means for sensing current flows comprises a first and a second current amplifier coupled to the first relay means and to the second relay means.
 4. The apparatus of claim 2 in which the first means for shunting the first diode includes a conductor extending from between the first terminal and the first diode to one of the contacts of the second pair of normally closed contacts of the second relay means, and conductor means extending from the other contact of the second pair of normally closed contacts of the second relay means respectively to the second terminal and to the first heating element.
 5. The apparatus of claim 4 in which the second means for shunting the second diode to provide full voltage to the second heating element includes a conductor extending from between the first terminal and the second diode to one contact of the first pair of normally closed contacts of the first relay means and conductor means extending from the other contact of the first pair of normally closed contacts of the first relay means respectively to the second terminal and to the second heating element.
 6. The apparatus of claim 5 in which the first heating circuit includes warning apparatus for sensing the interruption of current flow between the first terminal and the first heating element, and the second heating circuit includes warning means for sensing the interruption of current flow between the first terminal and the second heating element. 